1. Field of the Invention
This invention relates to an operation indicating member, and to a method of manufacturing the same. The term "operation indicating member" refers to that part of a key, push-button or the like, of the kind found on a switch-board, keyboard, input unit or table input unit, which indicates by means of a printed character the particular operating position or the information which will be entered by depressing the indicating member.
2. Description of the Prior Art
An example of the abovementioned operation indicating member is a key of the type which is used on the keyboard of a small electronic computer or the like. Such a key essentially comprises a dome-shaped push-button switch made of a rubber elastomer, and a contact member affixed to the undersurface of the push-button switch at the central portion thereof. The top surface of the push-button switch forms the key top which generally has a printed character such as a numeral or arithmetic symbol to indicate the function of the key. The character is printed by applying ink to the key-top surface of the push-button switch.
In the prior art, printing the character in the aforementioned manner is a difficult operation in cases where the key-top surface is not perfectly flat. Moreover, since the character will be raised slightly above the key-top surface owing to the application of the ink, the printed character will tend to be rubbed off with repeated usage, detracting from the appearance of the key and making it difficult to read.
The material most widely adopted to fabricate the rubber push-button switch is silicone rubber. This is because silicone rubber has excellent durability, resistance to heat and cold, a good coloring property, and because such properties as hardness and elasticity remain unchanged despite temperature variations. When the aforementioned rubber push-button switch is formed of silicone rubber, however, a new problem is added to those mentioned above, namely that printing is further complicated by the fact that the ink is difficult to apply to the key-top surface owing to the non-adherance property of silicone rubber. Furthermore, since the silicone rubber is printed following vulcanization, the undried ink tends to blur at its edges immediately after printing, thus making it difficult to print extremely fine lines. This is another problem which awaits solution.